Investigations of reading have focussed largely on two component processes, phonological processing and orthographic processing. However, a number of unresolved issues have hampered progress in the investigation of these abilities. Three such issues that formed the focus of the present study were (1) the extent to which tasks used to operationalise orthographic processing measure the same construct, (2) the extent to which tasks from a range of phonological processing domains measure the same construct, and (3) the degree to which orthographic processing tasks reflect orthographic processes independent of extraneous phonological operations, and conversely, phonological processing tasks measure phonological processes independent of orthographic processes. To address these questions, a variety of tasks used to evaluate orthographic processing (orthographic verification, homophone verification, nonlexical choice, irregular word reading, irregular word spelling), phonological processing (phoneme deletion, phonological choice, nonword reading, nonword spelling) and related domains (e.g., word identification, IQ) were administered to 177 children from Grades 3, 4 and 5. Factor analysis conducted using accuracy data revealed that orthographic processing tasks congregate along a single factor, while phonological processing tasks congregate along another, separate factor, viewed as evidence for the construct validity of orthographic processing and phonological processing, respectively. When response-time data were analysed, these same tasks did not differentiate on the basis of their orthographic and phonological demands, but rather in terms of their more general task demands. Additionally, results reveal that some phonological processing and orthographic processing tasks measure their respective construct with a greater degree of purity than do others. It is recommended that these tasks be used in future research.